In textile carding systems, the advantages of maintaining the uniformity of the sliver formed by the card, and reducing yarn count varaitions are well known. Conventional autoleveling to vary the rates of the speed of the doffer roll and the input feed roll in response to variations in the density of the sliver leaving the card is one familiar effort to improve sliver uniformity. Additionally, other efforts have been made to control the nature of the fiber batt that is fed to the card, to thereby improve the quality of end product of the card.
For example, systems are known in which the thickness of the batt formed by a fiber feeding device is sensed, and variations in the batt thickness are used to vary the speed of the discharge rolls through which the batt is fed from the fiber feeding device for delivery to the input of the card. It is also known, as disclosed in Erben U.S. Pat. No. 4,321,732, that the pressure of the collected fiber in a fiber feeding device may be used to vary the speed of inlet feed roll of such device, and, as disclosed in Krull U.S. Pat. No. 4,206,823, to sense the weight of the batt formed by a fiber feeder device and vary the speed of the discharge rolls of the fiber feeding device and the speed of the input rolls of the card. Also, in Beukent U.S. Pat. No. 3,896,523, a control system is disclosed by which the speed of the oscillation plate, or spanker plate, in the fiber feeding device is coordinated to vary proportionately to, and in dependence upon, the speed of the feeding means to the card.
In co-pending U.S. patent application Ser. No. 255,109, filed Apr. 17, 1981, now U.S. Pat. No. 4,387,486 a system is disclosed for improving sliver uniformity in which the spanker plate and inlet feed roll of a fiber feeder are normally operated at speeds which are proportional to the operating speed of the card, and the weight of the batt leaving the fiber feeder is sensed to generate a signal that is utilized to override the primary drive for the spanker plate and thereby vary the ratio between the operating speed of the spanker plate and the card. Additionally, the level of collected fiber in the fiber feeder is sensed to generate a signal that is utilized to override the primary drive of the inlet feed roll of the fiber feeder.
Finally, fiber feeding devices for forming batts have heretofore been provided with air pressure generating means, such as a blower, to improve the uniformity of the batt by compressing the fiber collected in the device and/or by equalizing the level of such collected fibers as disclosed for example in Husges U.S. Pat. No. 4,135,911, Hecker U.S. Pat. No. 3,482,883, and co-pending U.S. patent application Ser. No. 340,625, filed Jan. 19, 1982, now U.S. Pat. No. 4,476,611.
Thus, in general, the prior art discussed above falls into two categories, namely changing the card speed as the sliver density changes, or regulating the operations of the fiber feeding devices as the density of the batt delivered therefom varies. In the present invention, by contrast, the uniformity of the sliver is improved by sensing the density of the sliver and the batt, and directly controlling the compressing means in the fiber feeding devices to compensate for, and correct, the sensed variations in such densities.